System of pipes for use in oil wells

ABSTRACT

The present invention relates to pipes that convey any flowable medium, such as chemicals, food and in particular, oil and gas, and more particularly to a system of pipes having different coatings or linings for the interior and exterior surfaces of such pipes, depending on the environment in which the pipes are used. The pipes may be coated with different materials, which may be of different thicknesses, with various configurations of coatings or linings. Such coating may be done on the interior and/or the exterior of the pipes.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119 from U.S.Provisional Application Ser. No. 60/630,942, filed Nov. 24, 2004.

FIELD OF THE INVENTION

This invention relates to pipes that convey any flowable medium, such aschemicals, food and in particular, oil and gas, and more particularly toa system of pipes having different coatings or linings for the interiorand exterior surfaces of such pipes, depending on the environment inwhich the pipes are used.

BACKGROUND OF THE INVENTION

Pipes used in the production and transportation of flowable media aresubject to corrosion and plugging. An example of such a pipe is oil pipewhich is generally large and for reasons of economy is manufactured fromcarbon steel rather than more expensive corrosion resistant alloys.Corrosion is induced by the hot underground environment in whichdown-hole pipes convey oil from deeply buried deposits to the earth'ssurface. Materials such as water, sulfur, sulfur dioxide, carbondioxide, present in the oil typically make it acidic causing corrosionof the interior surface of the pipe. Even at cooler temperatures,transportation pipelines that extend for long distances close to theearth's surface experience the effects of corrosion because of the longcontact times involved. Corroded pipes are difficult and expensive toreplace.

Plugging occurs when organic materials soluble in the oil at hightemperatures of the oil deposit become insoluble as the oil cools duringthe rise through a pipe to the earth's surface. Plugging mayparticularly be a problem for offshore wells because the oil issubjected seawater temperatures. The resultant insoluble materials, suchas asphaltenes and paraffin waxes, tend to plate out of the oil at thehigh temperature of the oil deposit on the interior surface of the pipe,restricting the oil flow and eventually plugging the pipe. Also, solubleinorganic material, commonly referred to as scale and generallycomprising calcite and/or barite, present in the oil or in the presenceof salt water associated with conveying of oil from underground ofsubsea deposits, are present in the oil at the high temperature of theoil deposit. Plugging also occurs during long distance conveying of theoil through pipelines. Plugging requires that production ortransportation cease while the pipe is cleaned out either by mechanicalscraping (pigging), chemical treatment or hot oiling. Such cleaningreduces productivity and involves large maintenance costs. Similarproblems occur for pipes used in the manufacture and transportation ofcorrosive chemicals in the chemical processing industry.

Moreover, the environment exterior to the pipes in which oil well pipesare used will contribute to such pluggage and corrosion in oil pipes.For instance, when a pipeline is installed offshore on the sea floor itmay have high spots and low spots due to the undulation of the seafloor. In the low spots water may accumulate on the interior of thepipe. This water may come from hydrostatic testing of the pipeline orwater entrained in the fluids carried in the pipeline. Such water maycause corrosion if it penetrates the pipe. Also, the water may containcarbonic acid or hydrochloric acid. And occasionally oil and gas maycontain small amounts of corrosive gases such as carbon dioxide andhydrogen sulfide. When either of these gases are dissolved in water,acid is created that may attack the surface of the pipe. All of thesecauses may contribute to the failure of the pipe.

Solutions have been proposed in the oil industry for preventingcorrosion and pluggage by coating oil pipes on their interior surfaceand their exterior surfaces, see, for example, U.S. Pat. No. 6,397,895to Lively. This patent discloses the use of a phenolic primer incombination with an insulating layer and an abrasion resistant layerformed of an epoxy ceramic on the interior of a pipe. However, suchepoxies do not provide a particularly non-stick surface to the oil.Lining the interior surface of oil well pipes with a fluoropolymer, suchas polytetrafluoroethylene (PTFE), for example, as disclosed in EP 01910 092 to Mannesman Akt is known. Pope et al. in U.S. Pat. No.3,462,825 have previously described manufacturing a pipe with afluoropolymer liner. Such fluoropolymer linings present a non-sticksurface to the oil. However, because of this non-stick property, theselinings do not adhere particularly well to the interior surface of thepipe. In addition, the varying conditions of temperature, pressure andeven mechanical contacts can cause such linings to separate from theinterior surface, leading to loss in corrosion and possibly evennon-stick protection if the coating or lining ruptures. However, at thistime there does not exist a commercially attractive option for reducingpluggage and corrosion in pipes.

Thus, there remains a need for solving the problems of corrosion andplugging that occurs in pipes conveying flowable media, especially oilpipes, whether used in oil wells or for oil conveying. What would bedesirable is a pipe system which is tailored to the particularenvironment in which the pipes are used, where the interior surface ofsuch pipes resists the deposit of insoluble organic materials and hasresistance to the corrosive effects of acids, and the exterior surfaceinsulates the pipes in certain harsh environments. Further there is adesire that the interior and exterior surfaces be durable lasting formany years in harsh environments.

BRIEF SUMMARY OF THE INVENTION

The present invention satisfies the need for solving the problems ofcorrosion and pluggage in pipes by providing a system of pipes forconveying flowable media, especially an oil pipe, where differentsections of pipes are coated or lined on their interior and/or exteriorsurfaces with different materials in accordance with the demands of theenvironment in which the pipes are used.

Where used, the lining on the interior surface of the pipe presents anon-stick surface to the oil, whereby the insoluble organic materialspresent in the oil do not stick to the lining, and restriction of oilflow and pluggage is minimized or avoided. In addition, the lining onthe interior surface of the pipe is impermeable to salt water, as wellas to the corrosive materials present in the oil.

Where used, the lining on the exterior of the pipe protects the pipefrom the harsh effects of the environment. In addition, the lining onthe exterior of the pipe maintains the temperature difference betweenthe product inside the pipe and the product outside the pipe, whichhelps to keep the media in the pipe flowable.

It is an advantage of the present invention to be able to tailor the useof such linings so that particular problems may be addressed byparticular sections of pipe. In addition, with the present invention,certain sections of pipe need not be lined at al.

The lining system on the interior surface and/or exterior of the pipeeither minimizes or eliminates (i) the deposition of asphaltenes,paraffin wax, and inorganic scale, so as to minimize or eliminatepluggage of the oil pipe and (ii) corrosion of the interior surface ofthe pipe. The reduction in deposition can be characterized by being atleast 40%, preferably at least 50%, of at least one of asphaltenes,paraffin wax, and inorganic scale as compared to the interior surface ofthe pipe without the lining being present. Reductions of at least 60%,70%, 80% and even at least 90% may be realized. Preferably thesereductions apply to at least two of the deposition materials, and morepreferably, to all three of them. The reduced deposition performance ofthe lined pipes of the present invention is in contrast to the resultobtained for unlined pipes, as well as for epoxy resin-lined oil pipe,where surprisingly the deposition is greater than for the unlined pipe.This deposition reduction is accompanied by the added benefit of saltwater impermeability as well as corrosion resistance, as compared tounlined oil pipe.

The lining comprises a fluoropolymer, which has non-stick properties. Inone embodiment, the lining may comprise a perfluoropolymer, and inparticular, a pure perfluoropolymer. The pipe of this embodiment of thepresent invention has a continuous adherent perfluoropolymer coating, orlining, on its interior surface, with the exposed surface of theperfluoropolymer providing a non-stick surface for oil to flow freelythrough the pipe.

Because of the non-stick properties of fluoropolymer, however, thelining may not adhere particularly well to the interior surface of thepipe. Therefore, in a preferred embodiment, hereinafter referred to asthe primer layer/overcoat embodiment, the lining comprises a primerlayer adhered to the interior surface of the pipe and a fluoropolymerovercoat adhered to the primer layer. Instead of an overcoat, apreformed liner may be adhered to the primer layer. In either case, theintervening primer layer provides adhesion both to the overcoat and tothe interior surface of the pipe. The primer layer by itself does notprovide sufficient non-stick character and impermeability to thecorrosive materials present in the oil to protect the interior surfaceof the pipe from corrosion. With the combination of the primer layer andthe overcoat, the insoluble organic materials present in the oil do notstick to the lining, and restriction of oil flow and pluggage isminimized or avoided. In addition to presenting a non-stick surface tothe oil, the overcoat is impermeable to salt water, as well as to thecorrosive materials present in the oil.

In the primer layer/overcoat embodiment, either just the overcoat, orthe overcoat and the primer layer may be a perfluoropolymer. In thislatter case, the presence of perfluoropolymer in the primer layer, aswell as the overcoat, enables the overcoat to melt bond to the primerlayer when they are heated.

In order to enhance salt water impermeability as well as corrosionresistance as discussed above, the lining on the interior surface of thepipe may include particles which form a mechanical barrier againstpermeation of water, solvents and/or gases to the pipe.

Thus, in accordance with the present invention, there is provided asystem of pipes for conveying flowable media comprising a first pipe anda second pipe, where the second pipe has a lining adhered to theinterior surface of the pipe, and the lining of the second pipecomprises a primer layer adhered to the interior surface of the pipe andan overcoat or a preformed film comprising a fluoropolymer adhered tothe primer layer. Alternatively, the lining of the second pipe consistsessentially of a pure perfluoropolymer. According to one embodiment, abarrier layer may be formed between the primer layer and the overcoat,where the barrier layer includes a plurality of particles which form amechanical barrier against permeation of water, gases and solvents tothe pipe.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to pipes which convey flowable medium,and in particular to lining the interior of pipes and insulating theexterior of such pipes. Substrates suitable for pipes of this inventioninclude a wide variety of metal substrates such as aluminum, stainlesssteel, and especially metals that are not corrosion resistant such ascarbon steel.

The flowable medium may be a chemical, including paints andpharmaceuticals. Or the pipes may be useful in the food processingindustry, where the flowable medium is ketchup, peanut butter or creamcheese, where concern over antimicrobial buildup is an issue. Inaddition, the flowable medium may be gas, where there are no depositionconcerns, but corrosion is an issue. For this reason, and because thepresent invention is especially useful for metal substrates that are notcorrosion resistant, the present invention is particularly applicable todown-hole, i.e., oil well pipes, or above-ground pipeline systems, i.e.,oil-conveying pipes, oil pipes, where both deposition and corrosion areconcerns. Both types of pipes are generically referred to herein as oilpipes. The type and size of pipe is selected on the basis of use. Forinstance, the choice of pipe may depend on whether the pipe is used inthe oil well or to form an oil pipeline. If used as oil well pipes, thepipes are relatively large. Inner diameters of 2 in (5.08 cm), 2⅜ in(6.03 cm) and 3 in (7.6 cm) and larger and lengths of at least 20 ft(6.1 m) are quite common.

While the relative dimensions of the oil pipe are large, the thicknessof the lining on the interior surface of the pipe is quite small. Wherethe lining comprises a primer layer and an overcoat, the primer layerneeds only to be thin enough to adhere the overcoat layer to itself andthereby to the interior surface of the oil pipe. The overcoat willgenerally be from about 51 to 6350 micrometers (2 to 250 mils) thick,with the primer and overcoat coating thicknesses depending on how theselayers are formed and on the thickness desired for the particular oilpipe application. The primer layer of the oil pipe preferably is nogreater than 1 mil (25 micrometers) thick and the overcoat is preferably2 to 250 mils (51 to 6350 micrometers) thick. In applications where thincoatings are desired, the thickness of the overcoat is preferably 2-7mils (51-175 micrometers). In one preferred embodiment where the totalcoating thickness is relatively small, the overall coating thickness(primer layer thickness plus overcoat thickness) of the fluoropolymercoating being no greater than 8 mils (203 micrometers).

There is of course an economical advantage to supplying thin linings inapplications which are determined to be less severe. However, thicklinings are preferred in highly abrasive or in severely corrosiveenvironments. In those applications where thick coatings are preferred,the thickness of the overcoat is 25-250 mils (635-6350 micrometers),preferably 30-100 mils (762-2540 micrometers). In a preferred embodimentwhere the total coating thickness is relatively large, the overalllining thickness (primer layer thickness plus overcoat thickness) of thefluoropolymer coating is at least 26 mils (660 micrometers). Instead ofapplying an overcoat, thick linings may be achieved by forming apreformed perfluoropolymer film liner on the primer layer. The use ofpreformed film liner enables a relatively thick lining of uniformthickness to be formed.

The lining of the present invention comprises a fluoropolymer. In oneembodiment the lining of the present invention consists essentially of aperfluoropolymer. In a perfluoropolymer, the carbon atoms making up thepolymer chain, if not substituted by oxygen, are substituted withfluorine atoms. The end groups of the perfluoropolymer may also beentirely fluorine substituted, but other relatively stable end groups,such as —CF₂H and —CONH₂, may be present, especially in thefluoropolymer present in the primer layer. The perfluoropolymer used inthe present invention is melt flowable at the baking temperature, whichwill generally be in the range of 300° C. to 400° C.Polytetrafluoroethylene, which has a melt viscosity of at least 10⁸ Pa·sat 372° C., would not be melt flowable.

The perfluoropolymers used in the primer layer and the overcoat are meltflowable fluoropolymers. Examples of such melt-flowable fluoropolymersinclude copolymers of tetrafluoroethylene (TFE) and at least onefluorinated copolymerizable monomer (comonomer) present in the polymerin sufficient amount to reduce the melting point of the copolymersubstantially below that of TFE homopolymer, polytetrafluoroethylene(PTFE), e.g., to a melting temperature no greater than 315° C. Preferredcomonomers with TFE include the perfluorinated monomers such asperfluoroolefins having 3-6 carbon atoms and perfluoro(alkyl vinylethers) (PAVE) wherein the alkyl group contains 1-8 carbon atoms,especially 1-3 carbon atoms. Especially preferred comonomers includehexafluoropropylene (HFP), perfluoro(ethyl vinyl ether) (PEVE),perfluoro(propyl vinyl ether) (PPVE) and perfluoro(methyl vinyl ether)(PMVE). Preferred TFE copolymers include FEP (TFE/HFP copolymer), PFA(TFE/PAVE copolymer), TFE/HFP/PAVE wherein PAVE is PEVE and/or PPVE andMFA (TFE/PMVE/PAVE wherein the alkyl group of PAVE has at least twocarbon atoms). Typically, the melt viscosity will range from 10² Pa·s toabout 10⁶ Pa·s, preferably 10³ to about 10⁵ Pa·s measured at 372° C. bythe method of ASTM D-1238 modified as described in U.S. Pat. No.4,380,618. Typically these copolymers will have a melt flow rate of 1 to100 g/10 min as determined by ASTM D-1238 and ASTM tests applicable tospecific copolymers (ASTM D 2116-91a and ASTM D 3307).

Melt flowable polytetrafluoroethylene (PTFE), commonly referred to asPTFE micropowder, can also be present in the primer layer or theovercoat along with the melt-fabricable copolymers mentioned above, suchmicropowder having similar melt flow rate. Similarly, minor proportionsof non-melt-fabricable PTFE can be present either in the primer layer orthe overcoat, or both. In the primer layer the PTFE aids instratification towards providing a pure perfluoropolymer in the primerat the primer/overcoat interface. PTFE in the overcoat aids in coatingtoughness, but should not be used in proportions that detract from theimpermeability of the overall lining to corrosive fluids and theprotection of the pipe interior surface provided by the lining. Ineither case, the primer layer and the overcoat, while being polymerblends with either PTFE or multiple melt-flowable perfluoropolymers, arestill perfluoropolymers.

In the primer/overcoat embodiment, the overcoat comprises afluoropolymer. The fluoropolymer could be, but need not be aperfluoropolymer. In this embodiment, the primer layer may also, but notnecessarily, be comprise a perfluropolymer. In this case, othermaterials may be used for the primer layer as long as they promoteadhesion of the overcoat to the pipe.

The lining may be formed by a number of coating methods, such asapplication of liquid-based coating composition, application of powdercoating, and/or rotolining. In the primer layer/overcoat embodiment,different coating methods may be used for the primer layer and theovercoat. Preferred coating methods include liquid-based coatings forthe primer layer and the overcoat, or liquid-based coating for theprimer layer and powder coating for the overcoat, or and liquid-basedcoating for the primer layer and rotolining for the overcoat. Thecoating is heated to form the lining on the surface of the pipe. Theheating is optionally sufficient to bake the lining. This bakingconsolidates the lining from the dried liquid state or powder state to asolid film state. In the primer layer/overcoat embodiment, the primerlayer is baked, and the thickness of the primer layer after baking is nogreater than about 25 micrometers (1 mil). In this regard, the term“baking” is used in its broadest sense of achieving the aforesaidconsolidation. Sometimes, the term “curing” is used to describe thefilm-forming effect; “curing” is included within the meaning of the term“baking”. Typically, the baking is carried out by simply heating thelining sufficiently above the melting temperature of the material of thelining to cause the respective material to flow and fuse to become afilm-like layer. This allows the overcoat to adhere to the primer layer.In the primer layer/overcoat embodiment, this consolidation willgenerally involve baking of both of the primer layer and the overcoat,either sequentially or simultaneously. Exemplary of the effect of theconsolidation, in this embodiment, after the primer layer is baked andconsolidated, the thickness of the primer layer after baking is nogreater than about 25 micrometers (1 mil).

In the case of rotolining, as will be described below, the layer becomesfilm-like as it is formed. In the primer layer/overcoat embodiment, theprimer layer may only need to be partly consolidated, such as by dryingif applied as a liquid-based composition and possibly partially fused,with complete consolidation occurring upon baking of the overcoat.

The overcoat is impermeable to salt water, as well as to the corrosivematerials present in the oil and presents a non-stick surface to theoil, whereby the insoluble organic materials present in the oil do notstick to the overcoat lining, and restriction of oil flow and pluggageis minimized or avoided. Because of its non-stick property, however, theovercoat does not adhere to the interior surface of the pipe aftercontaminants are removed from the interior surface of the pipe. Theintervening primer layer provides adhesion both to the overcoat layerand to the interior surface of the pipe. The primer layer by itself doesnot provide sufficient non-stick character and impermeability to thecorrosive materials present in the oil to protect the interior surfaceof the pipe from corrosion.

In one preferred embodiment where the total coating thickness isrelatively small, the overall coating thickness (primer layer thicknessplus overcoat thickness) of the lining being no greater than 8 mils (203micrometers), the interior surface of the pipe is provided with anadherent coating that presents a non-stick surface to the oil andprovides a high degree of corrosion protection to the interior surface.In another preferred embodiment, the total coating thickness isrelatively thick, the overall lining thickness (primer layer thicknessplus overcoat thickness in the primer layer/overcoat embodiment) of thelining is at least 26 mils (660 micrometers).

To insure that a thin overcoat does not have pinholes through whichcorrosive material may pass to ultimately reach the interior surface ofthe pipe, the step of forming a lining is preferably carried out byapplying multiple coats or layers, one top of one another, where, in theembodiment where the lining comprises a primer layer and an overcoat,the overall thickness of the overcoat is still no greater than 7 mils(175 micrometers), preferably no greater than 6 mils (150 micrometers)in the case of using either liquid-based or powder coating overcoat. Thesucceeding coating application of the liquid or powder overcoatcomposition will fill in any pinholes present in the preceding overcoat.

In the primer layer/overcoat embodiment, the liquid basis of the coatingcomposition is preferably organic solvent, which avoids the creation ofrust on the cleaned and roughened interior surface of the pipe. Rustwould interfere with adhesion of the primer layer to the pipe interiorsurface The heating of the primer layer composition is sufficient to drythe composition to form the primer layer and may even be sufficient tobake the primer layer, prior to the formation of the overcoat. Theliquid basis of the overcoat composition is preferably water, tominimize the need for solvent recovery. In the case of the liquid-basedovercoat, following its application to the dried or baked primer layer,the overcoat is dried and then baked at a sufficiently high temperature,depending on the particular composition used, to melt the overcoatcomposition to be film forming and the composition of the primer layeras well if not already baked, bonding the primer layer to the overcoat.By “liquid-based” is meant that that the coating composition is in theliquid form, typically including a dispersion of perfluoropolymerparticles in the liquid, wherein the liquid is the continuous phase. Theliquid basis, i.e., the liquid medium can be water or organic solvent.In the case of forming the primer layer, the liquid basis is preferablyorganic solvent and in the case of the overcoat, the liquid basis ispreferably water. Organic solvent may, for example, be present in theovercoat liquid composition in a much smaller amount, e.g., no more than25% of the total weight of liquid, to improve wetting of the overcoatlayer and thereby improve application properties.

When the primer composition is applied as a liquid medium, the adhesionproperties described above will manifest themselves upon drying andbaking of the primer layer together with baking of the next-appliedlayer to form the non-stick coating on the pipe. When the primer layercomposition is applied as a dry powder, the adhesion property becomesmanifest when the primer layer is baked.

In the primer layer/overcoat embodiment, the composition of the primerlayer and the overcoat can be the same or different, provided that whenbaked together, they adhere to one another, and the primer layer adheresto the pipe. When the composition is the same, adequate intercoatadhesion is obtained. In a preferred embodiment, the primer layer andthe overcoat both comprise perfluoropolymers. The perfluoropolymers inthe primer layer and the overcoat are preferably independently selectedfrom the group consisting of (i) copolymer of tetrafluoroethylene withperfluoroolefin copolymer, the perfluoroolefin containing at least 3carbon atoms, and (ii) copolymer of tetrafluoroethylene with at leastone perfluoro(alkyl vinyl ether), the alkyl containing from 1 to 8carbon atoms. Additional comonomers can be present in the copolymers tomodify properties. Adequate intercoat adhesion is also obtained when oneof the perfluoropolymers is copolymer (i) and the other is copolymer(ii). The melting temperature of the lining will vary according to itscomposition. By melting temperature is meant the peak absorbanceobtained in DSC analysis of the lining. By way of example,tetrafluoroethylene/perfluoro(propyl vinyl ether) copolymer (TFE/PPVEcopolymer) melts at 305° C., whiletetrafluoroethylene/hexafluoropropylene melts at 260° C. (TFE/HFPcopolymer). Tetrafluoroethylene/perfluoro-(methyl vinylether)/perfluoro(propyl vinyl ether) copolymer (TFE/PMVE/PPVE copolymer)has a melting temperature in between these melting temperature. Thus, inone embodiment of the present invention, when the primer layer comprisesTFE/PMVE/PPVE copolymer and the perfluoropolymer in the overcoat isTFE/HFP copolymer, the baking of the overcoat may not be at a highenough temperature to bake the primer layer, in which case the primerlayer would be heated to the baked condition prior to applying theovercoat to the primer layer. Alternatively, the primer layer cancontain the lower melting perfluoropolymer, in which case the baking ofthe overcoat would also bake the primer layer.

A preferred ingredient in the primer layer, whether the primer isliquid-based or a dry powder, is a heat resistant polymer binder, thepresence of which enables the primer layer to adhere to the pipeinterior surface. The binder component is composed of polymer which isfilm-forming upon heating to fusion and is also thermally stable. Thiscomponent is well known in primer applications for non-stick finishes,for adhering the fluoropolymer-containing primer layer to substrates andfor film-forming within and as part of a primer layer. The fluoropolymerby itself has little to no adhesion to a smooth substrate. The binder isgenerally non-fluorine containing and yet adheres to the fluoropolymer.

Examples of the non-fluorinated thermally stable polymers includepolyamideimide (PAI), polyimide (PI), polyphenylene sulfide (PPS),polyether sulfone (PES), polyarylene-etherketone, andpoly(1,4(2,6-dimethylephenyl)oxide) commonly known as polyphenyleneoxide (PPO). These polymers are also fluorine-free and arethermoplastic. All of these resins are thermally stable at a temperatureof at least 140° C. Polyethersulfone is an amorphous polymer having asustained use temperature (thermal stability) of up to 190° C. and glasstransition temperature of 220° C. Polyamideimide is thermally stable attemperatures of at least 250° C. and melts at temperatures of at least290° C. Polyphenylene sulfide melts at 285° C. Polyaryleneether-ketonesare thermally stable at least 250° C. and melt at temperatures of atleast 300° C.

Examples of suitable powder coating compositions comprisingperfluoropolymer and polymer binder, wherein these components areassociated with one another in multicomponent particles are disclosed inU.S. Pat. Nos. 6,232,372 and 6,518,349.

The polymer binder can be applied as an undercoat to the pipe interiorsurface after treatment to remove contaminants and an organic solventsolution thereof, prior to application of the primer. The resultantdried thin film of polymer binder can further enhance the adhesion ofthe primer layer to the pipe interior surface.

For simplicity, only one binder may be used to form the binder componentof the composition of the present invention. However, multiple bindersare also contemplated for use in this invention, especially when certainend-use properties are desired, such as flexibility, hardness, orcorrosion protection. Common combinations include PAI/PES, PAI/PPS andPES/PPS. Typically, the polymer binder content on the primer layer willbe from 10-60 wt % based on the combined weight of the perfluoropolymerand polymer binder.

Other ingredients can be present in the primer, such as pigments,fillers, high boiling liquids, dispersing aids, and surface tensionmodifiers.

The lining composition can be applied to the interior surface of thepipe after removal of contaminants by spraying of the liquid-basedcomposition or dry powder from a nozzle at the end of a tube extendinginto the interior of the pipe and along its longitudinal axis. Thespraying starts at the far end of the pipe and is moved backward alongits longitudinal axis as the spray applies the liquid-based coating,until the entire interior surface is coated. The tube having the spraynozzle at its end is supported along its length and positioned axiallywithin the pipe by sled elements positioned along the length of thetube. As the tube and its nozzle is retracted from the pipe, the sledelements slide along the interior surface of the pipe, leaving theunderlying interior surface open to receive the sprayed coating. The drypowder primer can be sprayed using an electrostatic sprayer;electrostatic spraying is conventional in the dry powder coating art.

The preferred liquid which enables the lining composition to be a liquidis one or more organic solvents, within which the perfluoropolymer,present as particles in the preferred embodiment, is dispersed and thepolymer binder present either as dispersed particles or in solution inthe solvent. The characteristics of the organic liquid will depend uponthe identity of the polymer binder and whether a solution or dispersionthereof is desired. Examples of such liquids includeN-methylpyrrolidone, butyrolactone, methyl isobutyl ketone, high boilingaromatic solvents, alcohols, mixtures thereof, among others. The amountof the organic liquid will depend on the flow characteristics desiredfor the particular coating operation.

The solvent should have a boiling point of 50 to 200° C., so as not tobe too volatile at room temperature, but to be vaporized at reasonableelevated temperatures, less than the baking temperature of theperfluoropolymer. In the primer layer/overcoat embodiment, the thicknessof the primer layer is established by experience with the particularprimer composition selected and polymer binder concentrations and therelative amount of solvent that is present. Preferably the primercontains 40 to 75 wt % solvent based on the combined weight of solvent,polymer and polymer binder.

In an alternate embodiment, a powder overcoat is applied by rotolining.J. Scheirs, Modern Fluoropolymers, John Wiley & Sons (1997) describesthe rotolining process, which involves the adding of sufficientfluoropolymer in powder form to a steel vessel to coat the interiorsurface of the vessel with the desired thickness of the fluoropolymer,followed by rotating the vessel in three dimensions in an oven, to meltthe fluoropolymer, whereby the fluoropolymer covers the interior surfaceof the vessel and forms a seamless lining (p. 315). In the preferredmethod of this embodiment, the primer is heated sufficiently to both dryand bake the coating prior to rotolining. When the overcoat is arotolining, the preferred thickness of the lining is 30-220 mils(762-5588 micrometers), preferably 30-100 mils (762-2540 micrometers).

EP 0 226 668 B1 discloses the preparation of rotolining particles ofTFE/perfluoroalkyl vinyl ether (PAVE) in which the vinyl ether comonomercontains 3 to 8 carbon atoms, disclosing particularly perfluoro(methylvinyl ether), perfluoro(propyl vinyl ether), and perfluoro(heptyl vinylether). Such particles can be used in this invention. The TFE/PAVEcopolymer particles used in the present invention can also be made byother processes, for example the melt extrusion of the copolymer andcutting of the extrudate into minicubes as disclosed in U.S. Pat. No.6,632,902. The average particle size of the copolymer particles used forrotolining in the present invention is preferably about 100 to 3000 μm,more preferably about 400 to 1100 μm.

The rotolining method of forming the lining can be used to form both theprimer and overcoat layers. When forming the primer, it is preferredthat the fluoropolymer primer composition also contain a finely dividedmetal additive such as Zn or Sn in an amount of about 0.2 to 1 wt %based on the combined weight of the metal powder and fluoropolymer. Thisadditive, in place of polymer binder, enables the rotolining primer toadhere to the pipe interior surface. Because it is more economical toform a thin primer layer by using a liquid-based primer composition, itis preferred that the rotolining technique be used for the formation ofthe overcoat layer, especially when a thick overcoat is desired, such asdescribed above.

The overcoat can also be applied as a liquid perfluoropolymercomposition, i.e., powder particles having an average particle size of 2to 60 micrometers dispersed or solubilized in an organic solvent ordispersed in aqueous media. However, the overcoat is preferably appliedas a powder composition by means of known spray devices such as byelectrostatic spraying. The overcoat does not require any ingredienttherein to promote adhesion to the interior surface of the oil pipe,because the primer layer provides this adhesion and adhesion to theovercoat. Therefore the overcoat composition applied to the primer layercan be essentially free of any other ingredient, preferably providing apure perfluropolymer interior surface facing the oil in the oil pipe, toprovide the best non-stick surface.

In another embodiment, the lining comprises a barrier layer whichincludes a plurality of particles which form a mechanical barrieragainst permeation of water, solvents and/or gases to the pipe. Thebarrier layer has a typical thickness of about 1 to about 10 mils(25-254 micrometers). Preferably the barrier layer comprises afluoropolymer and a platelet shaped filler particle that are relativelyinert to chemical attack. The particles form a mechanical barrieragainst permeation of water, solvent and oxygen to the substrate and arepresent in the amount of about 2 to about 10% by weight based on thetotal dry weight of the barrier layer. In spray application, theparticles tend to align parallel to the interior surface of the pipe.Since oxygen, solvent and water cannot pass through the particlesthemselves, the presence of aligned particle particles further reducesthe rate permeation through the lining which is formed.

Examples of typical platelet shaped filler particles include mica, glassflake and stainless steel flake. It is also within the scope of thisinvention that the lining may contain platelet shaped filler particleswith or without the presence of an intermediate barrier layer.

The platelet shaped particles of filler component of the barrier layerare preferably mica particles, including mica particles coated with anoxide layer like iron or titanium oxide. These particles have an averageparticle size of about 10 to 200 microns, preferably 20-100 microns,with no more than 50% of the particles of flake having average particlesize of more than about 300 microns. The mica particles coated withoxide layer are those described in U.S. Pat. No. 3,087,827 (Klenke andStratton); U.S. Pat. No. 3,087,828 (Linton); and U.S. Pat. No. 3,087,829(Linton).

The micas described in these patents are coated with oxides or hydrousoxides of titanium, zirconium, aluminum, zinc, antimony, tin, iron,copper, nickel, cobalt, chromium, or vanadium. Mixtures of coated micascan also be used.

In the primer layer/overcoat embodiment, when a barrier layer is used,the overcoat includes a multiple coating of a first-applied coating onthe primer layer to form a lower layer of the overcoat of afluoropolymer, preferably perfluoropolymer, composition containing asmall amount of mica dispersed therein, followed by a subsequent appliedcoating on the perfluoropolymer/mica lower layer of fluoropolymer,preferably perfluoropolymer, to form a perfluoropolymer upper layer thatis free of mica. Each of these layers can be applied by powder coatingor by liquid coating. Further details on the perfluoropolymer/micacomposition is disclosed in U.S. Pat. No. 5,972,494, wherein it isdisclosed that the mica constitutes 2 to 15 wt % of the composition and0.5 to 1.5 wt % of talc may also be present. For purposes of the presentinvention, these percents refer to the combined weight of theperfluoropolymer and the mica and the talc, if present. The presence ofthis lower layer further improves the impermeability performance of thelining when the corrosive conditions in particular oil wells requireenhanced protection of the oil pipe.

In the preformed film embodiment, a preformed film liner is inserted inthe pipe, instead of coating the pipe with a lining. The use ofpreformed film enables a relatively thick lining of uniform thickness tobe formed. The preformed film is sufficiently thick and defect free soas to minimize the passage of corrosive material to the interior surfaceof the pipe.

The preformed film does not adhere to the interior surface of the pipe,so a primer layer is used with this embodiment. The intervening primerlayer as described above provides adhesion both to the preformed filmand to the interior surface of the pipe. However, the primer layer byitself does not provide sufficient nonstick character and impermeabilityto the corrosive materials present in the oil to protect the interiorsurface of the pipe from corrosion. The use of both a primer and apreformed film liner has the benefit of providing good adhesion to theinterior metal surface yet allowing for the desirable thickness apreformed film in particular can provide.

The preformed film is preferably made of a fluoropolymer. The presenceof fluoropolymer in the preformed film provides both excellentimpermeability and nonstick character. The primer layer may alsocomprise a fluoropolymer. The presence of fluoropolymer in the primerlayer enables the preformed film to fusion bond to the primer layer inthe carrying out of the baking step.

The fluoropolymer in the primer layer, barrier layer and preformed filmis independently selected from the group of polymers and copolymers oftrifluoroethylene, hexafluoropropylene, monochlorotrifluoroethylene,dichlorodifluoroethylene, tetrafluoroethylene, perfluorobutyl ethylene,perfluoro(alkyl vinyl ether), vinylidene fluoride, and vinyl fluorideand blends thereof and blends of said polymers with a nonfluoropolymer.The fluoropolymers used in this invention are preferablymelt-processible. By melt-processible it is meant that the polymer canbe processed in the molten state (i.e., fabricated from the melt intoshaped articles such as films, fibers, and tubes etc. that exhibitsufficient strength and toughness to be useful their intended purpose).Examples of such melt-processible fluoropolymers include copolymers oftetrafluoroethylene (TFE) and at least one fluorinated copolymerizablemonomer (comonomer) present in the polymer in sufficient amount toreduce the melting point of the copolymer substantially below that ofTFE homopolymer, polytetrafluoroethylene (PTFE), e.g., to a meltingtemperature no greater than 315° C. Such fluoropolymers includepolychlorotrifluoroethylene, copolymers of tetrafluoroethylene (TFE) orchlorotrifluoroethylene (CTFE). Preferred comonomers of TFE areperfluoroolefin having 3 to 8 carbon atoms, such as hexafluoropropylene(HFP), and/or perfluoro(alkyl vinyl ether) (PAVE) in which the linear orbranched alkyl group contains 1 to 5 carbon atoms. Preferred PAVEmonomers are those in which the alkyl group contains 1, 2, 3 or 4 carbonatoms, and the copolymer can be made using several PAVE monomers.Preferred TFE copolymers include FEP (TFE/HFP copolymer), PFA (TFE/PAVEcopolymer), TFE/HFP/PAVE wherein PAVE is PEVE and/or PPVE and MFA(TFE/PMVE/PAVE wherein the alkyl group of PAVE has at least two carbonatoms). The melt-processible copolymer is made by incorporating anamount of comonomer into the copolymer in order to provide a copolymerwhich typically has a melt flow rate of about 1-100 g/10 min as measuredaccording to ASTM D-1238 at the temperature which is standard for thespecific copolymer. Typically, the melt viscosity will range from 10²Pa·s to about 10⁶ Pa·s, preferably 10³ to about 10⁵ Pa·s measured at372° C. by the method of ASTM D-1238 modified as described in U.S. Pat.No. 4,380,618. Additional melt-processible fluoropolymers are thecopolymers of ethylene or propylene with TFE or CTFE, notably ETFE,ECTFE, PCTFE, TFE/ETFE/HFP (also known as THV) and TFE/E/HFP (also knownas EFEP). Further useful polymers are film forming polymers ofpolyvinylidene fluoride(PVDF) and copolymers of vinylidene fluoride aswell as polyvinyl fluoride (PVF) and copolymers of vinyl fluoride.

While the fluoropolymer component is preferably melt-processible,polytetrafluoroethylene (PTFE) including modified PTFE which is notmelt-processible may be used together with melt-processiblefluoropolymer or in place of such fluoropolymer. By modified PTFE ismeant PTFE containing a small amount of comonomer modifier whichimproves film forming capability during baking (fusing), such asperfluoroolefin, notably hexafluoropropylene (HFP) or perfluoro(alkylvinyl) ether (PAVE), where the alkyl group contains 1 to 5 carbon atoms,with perfluoro(ethyl vinyl) ether (PEVE) and perfluoro(propyl vinyl)ether (PPVE) being preferred. The amount of such modifier will beinsufficient to confer melt fabricability to the PTFE, generally no morethan 0.5 mole %. The PTFE, also for simplicity, can have a single meltviscosity, usually at least 1×10⁹ Pa·s, but a mixture of PTFE's havingdifferent melt viscosities can be used to from the fluoropolymercomponent. Such high melt viscosity indicates that the PTFE does notflow in the molten state and therefore is not melt-processible.

The fluoropolymers in the primer layer, preformed film and barrier layercan be the same or different, provided that when baked together, theyadhere to one another. The fluoropolymer in the primer layer and barrierlayer used in this invention is preferably independently selected frommelt processible fluorinated ethylene/propylene copolymer,ethylene/tetrafluoroethylene copolymer, andtetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer. Thefluoropolymer in the preformed film of this invention is preferablyselected from polyvinyl fluoride(PVF), fluorinated ethylene/propylenecopolymer, ethylene/tetrafluoroethylene copolymer,tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer,polyvinylidene fluoride and a blend of polyvinylidene fluoride and anacrylic polymer, preferably nonfluoropolymer acrylic polymer.

As in the coating embodiment as described above, a preferred ingredientin the primer is a heat resistant polymer binder, the presence of whichenables the primer layer to adhere to the interior surface of the pipe.The binder component is composed of polymer which is film-forming uponheating to fusion and is also thermally stable. This component is wellknown in primer applications for nonstick finishes, for adhering thefluoropolymer-containing primer layer to substrates and for film-formingwithin and as part of a primer layer. The fluoropolymer by itself haslittle to no adhesion to the interior surface of the metal pipe. Thebinder is generally non-fluorine containing and yet adheres to thefluoropolymer.

Examples of the non-fluorinated thermally stable polymer binders includepolyamideimide (PAI), polyimide (PI), polyphenylene sulfide (PPS),polyether sulfone (PES), polyarylene-etherketone, polyetherimide, andpoly(1,4(2,6-dimethylephenyl)oxide) commonly known as polyphenyleneoxide (PPO). These polymers are also fluorine-free and arethermoplastic. All of these resins are thermally stable at a temperatureof at least 140° C. Polyethersulfone is an amorphous polymer having asustained use temperature (thermal stability) of up to 190° C. and glasstransition temperature of 220° C. Polyamideimide is thermally stable attemperatures of at least 250° C. and melts at temperatures of at least290° C. Polyphenylene sulfide melts at 285° C. Polyaryleneether-ketonesare thermally stable at least 250° C. and melt at temperatures of atleast 300° C. When the primer composition is applied as a liquid medium,the adhesion properties described above will manifest themselves upondrying and baking of the primer layer together with baking of the nextapplied layer of fluoropolymer to form the nonstick coating of thesubstrate.

The polymer binder can be applied as an undercoat to the pipe interiorsurface after treatment to remove contaminants and a solvent solutionthereof, prior to application of the primer. The resultant dried thinfilm of polymer binder can further enhance the adhesion of the primerlayer to the pipe interior surface.

For simplicity, only one binder resin may be used to form the bindercomponent of the primer composition of the present invention. However,multiple binder resins are also contemplated for use in this invention,especially when certain end-use properties are desired, such asflexibility, hardness, or corrosion protection. Common combinationsinclude PAI/PES, PAI/PPS and PES/PPS.

Other ingredients can be present in the primer, such as pigments,fillers, high boiling liquids, dispersing aids, and surface tensionmodifiers.

The primer layer is preferably liquid-based. The liquid basis of theprimer coating is preferably an organic solvent. Although water-basedprimers may be used in some applications, the use of solvent deters thecreation of rust on the interior surface of the pipe which may interferewith adhesion of the primer layer to the surface of the pipe.

The preferred liquid which enables the primer to be a liquid compositionis one or more organic solvents, within which the fluoropolymer, presentas particles, are dispersed and the polymer binder present either asdispersed particles or in solution in the solvent. The characteristicsof the organic liquid will depend upon the identity of the polymerbinder and whether a solution or dispersion thereof is desired. Examplesof such liquids include N-methylpyrrolidone, butyrolactone, methylisobutyl ketone, high boiling aromatic solvents, alcohols, mixturesthereof, among others. The amount of the organic liquid will depend onthe flow characteristics desired for the particular coating operation.

The solvent should have a boiling point of 50 to 200° C., so as not tobe too volatile at room temperature, but to be vaporized at reasonableelevated temperatures, less than the baking temperature of thefluoropolymer. The thickness of the primer layer coating is establishedby experience with the particular primer composition selected, includingits fluoropolymer and polymer binder concentrations and the relativeamount of solvent that is present. The primer layer of the oil pipepreferably has a thickness of in the range of 5-100 micrometers,preferably 10-30 micrometers. Preferably the primer contains 40 to 75 wt% solvent based on the combined weight of solvent, fluoropolymer andpolymer binder.

Powder coatings may also be used for the primer layer in the preformedfilm embodiment. Examples of suitable powder coating compositionscomprising perfluoropolymer and polymer binder, wherein these componentsare associated with one another in multicomponent particles aredisclosed in U.S. Pat. Nos. 6,232,372 and 6,518,349. When the primer isapplied as a dry powder, the adhesion property becomes manifest when theprimer layer is baked.

When a non-melt-processible fluoropolymer is used for the preformedliner, the liner can be made, for example, by methods including pasteextrusion as described in U.S. Pat. No. 2,685,707. In paste extrusion, apaste extrusion composition is formed by mixing PTFE fine powder with anorganic lubricant which has a viscosity of at least 0.45 centipoise at25° C. and is liquid under the conditions of subsequent extrusion. ThePTFE soaks up the lubricant, resulting in a dry, pressure coalescingpaste extrusion composition that is also referred to as lubricated PTFEfine powder. During paste extrusion which is typically performed at atemperature of 20 to 60° C., the lubricated fine powder is forcedthrough a die to form a lubricated green extrudate. The lubricated greenextrudate is then heated, usually at a temperature of 100 to 250° C., tomake volatile and drive off the lubricant from the extrudate. In mostcases, the dried extrudate is heated to a temperature close to or abovethe melting point of the PTFE, typically between 327° C. and 500° C., tosinter the PTFE.

Alternatively, granular PTFE can be isostatically molded or ram extrudedinto a tubular liner and fitted into a pipe housing to form thepreformed liner. In this embodiment, the liner is processed to a sizesomewhat larger than the inner diameter (I.D.) of the steel housing intowhich it is being installed. The thickness is typically 50-120 mil. Theliner is preferably pulled through a reduction die into a pipe that haseither an adhesive applied thereto. A programmed heating cycle relaxesthe liner inside the steel housing, resulting in a snug liner fit.

The preformed film is preferably in the shape of tubular liner with theouter diameter of the tube being greater than the interior diameter ofthe pipe to be lined. In a preferred embodiment the initial outerdiameter of said tubular liner is about 10 to 15% greater than the innerdiameter of the pipe. In a more preferred embodiment, the tubular lineris applied to the interior surface of the pipe according to theteachings of U.S. Pat. No. 3,462,825 (Pope et al.) by gripping one endof the liner, pulling the liner into the oil pipe through a reductiondie (or reducing the outer diameter through some other mechanicalmeans), releasing the liner and allowing the liner to expand into tightengagement with the primer layer (or barrier layer, if present) of theinterior surface of the pipe. The pipe is subsequently baked to insurefusion bonding of the liner to the primer layer which adheres to theinterior surface of the pipe. The baking of the primer layer (andbarrier layer if present) and the fusion bonding of this layer to thepreformed film is carried out by placing the pipe in an oven and heatingthe entire pipe sufficiently to cause baking and or fusion bonding tooccur.

Although Pope et al. have previously described manufacturing a pipe witha fluoropolymer liner, there are deficiencies in those teaching whentrying to apply them to pipes of this invention. The lining applied inthis way may not be tight and therefore pressure drops in the use of thelined pipe may cause the lining to buckle pulling away from the interiorsurface allowing accumulation of gases and liquids between the liner andthe wall surface and narrowing the path of oil flow. With the presentinvention, such buckling is prevented because of the presence of aprimer layer on the pipe's interior surface bonding the film to theinterior surface. It is unexpected that the fluoropolymer film adheresto the primer coating. The bonding of the film to the primer layerinvolves the heating of the pipe sufficiently to melt the primer/filminterface and then cooling the pipe. The film has a greater shrinkageduring cooling than the pipe, which would tend to pull the film awayfrom the primer layer. Nevertheless, the bond achieved in the moltencondition remains intact, resulting in the film forming a lining that isbonded to the pipe through the intervening primer (or barrier) layer.The expansion of the film during the heating step, while theoreticallygreater than the expansion of the pipe, is limited by the relaxationeffect of the heating of the film to the molten or near moltencondition. The shrinkage of the film during cooling starts from thisrelaxed condition and then outpaces the shrinkage of the pipe. Underthis condition, it is surprising that the molten bond retains itsintegrity during cooling. In a the present invention, the expansion fitof the Pope et al. approach for lining a pipe is replaced by a fusionbonded liner that resists separation and buckling characteristic ofunbonded liners.

Further according to the present invention, an exterior lining is formedon the exterior surface of the pipe. The amount and the type of liningon the exterior of the pipe is determined by the temperature andchemical makeup of the fluids to be transported. For instance, if theproduct has a substantial portion of its constituents that wouldcrystallize or form hydrates, or in another way come out of the fluid attemperatures below the temperatures coming out of the wellhead, then theproduct must be desirably kept above the temperature at whichcrystallization would occur. Even if the product is substantially devoidof such constituents, but would rise in viscosity at temperaturesapproaching that of the lower ambient environment, it is advantageous toreduce of eliminate the viscosity rise by the use of an exterior lining.In addition, there may be other reasons or combinations of reasons toinsulate pipes and pipelines. For instance, in particularly corrosivesubsea environments, it may be desirable to use a lining on the exteriorof the pipe to protect against corrosion.

The exterior lining may comprise a fluoropolymer coating, such asdescribed above for the interior of the pipe, and in particular, aperfluoropolymer coating, or it may comprise a preformed film, asdescribed above. In addition, the exterior lining may comprise aurethane foam, a polyurethane foam, hollow glass microspheres, orepoxies, such as in powder coating form, maleic anhydride, or anymaterial which demonstrates excellent adhesion, resistance to thermaland mechanical shock, and excellent chemical and physical resistance ina wide range of crude and refined petroleum products. The exteriorlining may be a two-part or layer system, or a one-part of layer system.In particular, epoxies are used in a two-part system, and maleicanhydride is used in a one-part system. In addition, adhesive and tape(e.g., vinyl or polyethylene), wrapping, powder coatings, extrudedplastic (such as polyurethane, polyolefins, vinyl and the like) extrudedelastomers (ethylene propylene rubber, butyl rubber, nitrite rubber,polychloropropene rubber and the like) and combinations of thesetechniques, as disclosed in U.S. Pat. No. 6,397,895. A non-wovenmaterial with an interspersed gel for wrapping pipes is disclosed inU.S. Patent Application Publication No. 2002/0094426 is also suitablefor the exterior lining of the present invention.

The total thickness of the exterior lining may be greater than or equalto 2 mils, up to about 100 mils. This thickness may be achieved by oneor more layers. These layers may be the same or different thicknesses.The thickness of the exterior lining can be tailored to a specificservice, as described above with respect to the thickness of theinterior coating. The temperature differences between the environmentand the fluid product, as well as the temperature at which the fluidproduct is desired to be maintained or deliver, will be determinative ofthe amount of exterior insulation, as well thickness and/or number oflining layers and primer and overcoat used. By thickness is meant notonly total thickness, but also the number of layers making up the totalthickness. These layers may be equal or unequal in their thickness.

According to a novel aspect of the present invention, differentcombinations of the above-described coatings or linings may be useddifferent sections of pipe, depending on the demands of the environment.For instance, a fluoropolymer may be used in the lower region of an oilwell, where asphaltenes deposit. FEP may be used in coated sections toinhibit paraffin deposit in the upper 1500 feet of a well. Where scaleis a problem a different fluoropolymer may be used. Epoxy may be used inthe sections of pipes in areas where plugging is not as much of aproblem but where corrosion is an issue. In addition, various sectionsof the pipe system may be insulated on the exterior to inhibitcorrosion, especially in off shore piping system.

Also, depending on the environment in which the pipes are used,different thicknesses may be used to coat the interior surface of thepipes in different zones. For instance, in particularly corrosiveenvironments, thicker linings are desired. In such circumstances, it maybe useful to provide a pre-formed lining instead of a coating system.

A pipe is lined according to the present invention as follows.Preferably the interior surface of the pipe is subjected to cleaningand/or grit-blasting to improve adhesion of the fluoropolymer lining tothe interior surface. The interior surface of the oil pipe, asmanufactured is generally smooth but with peaks and valleys and isgenerally coated with preservative to minimize any rusting. Beforeapplying the fluoropolymer lining on the pipe interior surface, suchsurface is typically cleaned to remove the preservative. Conventionalsoaps and cleansers can be used. The pipe can be further cleaned bybaking at high temperatures in air, temperatures of 800° F. (427° C.) orgreater. The cleaned interior surface is then preferably grit blasted,with abrasive particles, such as sand or aluminum oxide, to form aroughened surface to improve the adhesion of the primer layer. The gritblasting is sufficient to remove any rust that may be present. Theroughening that is desired for primer layer adhesion can becharacterized as a roughness average of 70-250 microinches (1.8-6.4micrometers).

In a preferred embodiment, where a primer layer and overcoat is used,the primer is applied to the cleaned, grit-blasted interior surface ofthe pipe by spraying a liquid-based composition from a nozzle at the endof a tube extending into the interior of the pipe and along itslongitudinal axis. The primer is preferably applied to a heated pipe inorder to prevent running, dripping and sagging.

Typically the pipe is preheated to 110-125° F. (43-52° C.) but highertemperatures may be used providing that they are about 20° F. below theboiling point of the solvent of the composition. The spraying starts atthe far end of the pipe and is moved backward along its longitudinalaxis as the spray applies the liquid-based coating, until the entireinterior surface is coated. The tube having the spray nozzle at its endis supported along its length and positioned axially within the pipe bysled elements positioned along the length of the tube. As the tube andits nozzle is retracted from the pipe, the sled elements slide along theinterior surface of the pipe, leaving the underlying interior surfaceopen to receive the sprayed coating.

The lining is applied to the interior surface of a pipe according to apreferred embodiment of the present invention, where a primer layer andovercoat are applied, as follows. The primer can be applied to theinterior surface of the pipe after removal of contaminants by sprayingof the liquid-based composition or dry powder from a nozzle at the endof a tube extending into the interior of the pipe and along itslongitudinal axis. The spraying starts at the far end of the pipe and ismoved backward along its longitudinal axis as the spray applies theliquid-based coating, until the entire interior surface is coated. Thetube having the spray nozzle at its end is supported along its lengthand positioned axially within the pipe by sled elements positioned alongthe length of the tube. As the tube and its nozzle is retracted from thepipe, the sled elements slide along the interior surface of the pipe,leaving the underlying interior surface open to receive the sprayedcoating. The dry powder primer can be sprayed using an electrostaticsprayer; electrostatic spraying is conventional in the dry powdercoating art.

After application of the primer to the interior surface of the pipe, thetube and nozzle are removed and the pipe is subjected to a heating stepto at least dry the primer to form the primer layer. Typically, the pipewill be placed in an oven heated to an elevated temperature to vaporizethe solvent or to heat the pipe and its primer layer to a highertemperature, above the melting temperature of the primer layer to bakethe primer layer.

After the heating step, the overcoat is spray-applied as a liquid-basedcomposition or as a dry powder onto the primer layer, using a tubesupported by sled elements and nozzle similar to that used to apply theprimer. It has been found that mere drying of the liquid-based primer toform the primer layer may give the layer adequate integrity towithstand, i.e. not be removed by, the sliding of the sled elementsacross the primer layer surface as the tube/spray nozzle are retractedduring spraying of the liquid-based overcoat. To accomplish multipleapplications of the overcoat to the primer layer, the overcoat appliedin one spray application is baked so that the subsequent spayapplication can be carried out without the sled elements scaring orotherwise removing overcoat from the preceding application. In the caseof the overcoat being a dry powder, the resultant powder coating shouldbe baked before the next spray application of dry powder if greatercoating thickness is desired.

When the primer composition is applied as a liquid medium, the adhesionproperties described above will manifest themselves upon drying andbaking of the primer layer together with baking of the next-appliedlayer to form the non-stick coating of the substrate. When the primer isapplied as a dry powder, the adhesion property becomes manifest when theprimer layer is baked.

The pipe is then baked to melt the overcoat, again by placing the pipein an oven heated to the desired temperature. Typically, the bakingtemperature applied to the overcoat through the thickness of the wall ofthe pipe and the primer layer, will be at least 20° C. above the meltingpoint of the overcoat, with the temperature and time of exposure beingsufficient to bake the overcoat. The same is true with respect to thebaking of the primer layer.

The heating of the primer coating is sufficient to dry the coating toform the primer layer and may even be sufficient to bake the primerlayer, prior to application of the preformed film. By “baking” is meantthat the fluoropolymer layer is heated sufficiently at a temperatureabove its melting temperature to cause the fluoropolymer to flow andform a continuous film-like layer. By melting temperature is meant thepeak absorbance obtained in DSC analysis of the fluoropolymer. Thebarrier layer if used is applied in the same way as the primer layer andmay be heated with the primer layer or applied to a dry primer layer andthen heated to drying or baking prior to application of the lining.

By “fusion bonding” is meant that the pipe is heated sufficiently tomelt bond the overcoat or preformed film to the primer layer orintervening barrier layer. That is to say, that the primer/overcoat orfilm interface, or the interfaces of the primer layer/barrierlayer/overcoat or preformed film as the case may be, are melted togethersufficiently to adhere the overcoat firmly to the layer(s). Fusionbonding temperatures are dependent on the particular fluoropolymerpresent in the or overcoat or preformed film. For PFA or FEP, the pipeis heat (baked) by conventional means to a temperature between 600 to700° F. (315 to 371° C.). For ETFE, the pipe is heated by conventionalmeans to a temperature between 550° to 630° F. (228 to 332° C.). Timefor fusion bonding will be dependent on the baking temperature used butis typically from 5 minutes to 60 minutes. Baking time and temperaturemust be sufficient to achieve a firm melt bond between the overcoat orpreformed film and the primer or barrier layer. As the pipe cools, thereis a tendency for the preformed film to shrink. Unexpectedly, theintercoat bonding between the primer layer (and barrier layer, ifpresent) and the overcoat or preformed film is sufficient to prevent thefilm from pulling away from the primer layer or barrier layer.

The melting temperature of the lining will vary according to itscomposition. By melting temperature is meant the peak absorbanceobtained in DSC analysis of the lining. By way of example,tetrafluoroethylene/perfluoro(propyl vinyl ether) copolymer (TFE/PPVEcopolymer) melts at 305° C., whiletetrafluoroethylene/hexafluoropropylene melts at 260° C. (TFE/HFPcopolymer). Tetrafluoroethylene/perfluoro-(methyl vinylether)/perfluoro(propyl vinyl ether) copolymer (TFE/PMVE/PPVE copolymer)has a melting temperature in between these melting temperature. Thus, inone embodiment of the present invention, when the primer layer comprisesa perfluoropolymer which is TFE/PMVE/PPVE copolymer and the overcoatcomprises a perfluoropolymer which is TFE/HFP copolymer, the baking ofthe overcoat may not be at a high enough temperature to bake the primerlayer, in which case the primer layer would be heated to the bakedcondition prior to applying the overcoat to the primer layer.Alternatively, the primer can contain the lower meltingperfluoropolymer, in which case the baking of the overcoat would alsobake the primer layer.

The exterior lining is formed on the exterior surface of the pipe afterthe interior lining is formed. The exterior lining may be wrapped aroundthe exterior of the pipe, or in the case of a preformed exterior liner,may be slipped over the pipe.

The resultant pipe has a continuous adherent lining on its interiorsurface, with the exposed surface of the lining, which is preferablyperfluoropolymer, providing a non-stick surface for oil to eventuallyflow through the pipe and for its constituents. The lining follows thepeaks and valleys of the interior surface of the pipe and to some extentfills them in with the primer and overcoat layers. The lining both actsas a non-stick surface for the oil and its constituents, but also toisolate the steel structure of the pipe from corrosion. The interiorlining provides a degree of insulation to the pipe. The exterior liningprovides an additional degree of insulation.

The use of different systems of pipe according to the present inventionprovides a degree of flexibility, so that different combinations of theabove-described coatings or linings may be used different sections ofpipe, depending on the demands of the environment. This provides forimproved pluggage reduction and corrosion resistance. In additionbecause certain sections of pipe need not be lined at all, this reducesthe cost associated with designing a pipes for oil wells or for oilconveying systems.

The pipes of the present invention are able to withstand conditions ashigh s 350° F. (177° C.) and 20,000 psi (138 MPa) present in some hightemperature/high pressure reserves. The invention is also applicable topipe used in the Chemical Processing Industry (CPI), especially in thoseapplications where temperatures such as those described above areencountered. In the CPI temperatures of at least about 350° F. (177° C.)and even as high as 400° F. (204° C.) are used. The pipes show superiorpermeation resistance to corrosive chemicals due to both to theirconstruction, i.e., especially when a primer layer and overcoat orprimer layer and preformed film liner are used, and especially with anoptional intervening barrier layer, and their strong adherence to theinterior surface of the pipe with the aid of a primer. In prior artsystems where only a film liner is present, gas is able to permeatethrough the film to both corrode the pipe and to exert pressure on thefilm from the metal interface side of the film. This results inblistering at the metal interface and eventual buckling of the film toconstrict and possibly block the interior of the pipe. In particular, inthe preformed liner embodiment of the present invention, pipes of thepresent invention are able to deter the permeation of gases and vaporsand resist the accumulation of chemicals at the interface of the metaland primer/film greatly retarding catastrophic failure. The lined pipesof the present invention are able to withstand the above describedconditions for continuous service, e.g., for at least 30 days,preferably at least 60 days, and more preferably at least 12 months.

Because of all the above-noted advantages, the present invention iscapable of reducing the deposition of at least one of asphaltenes,paraffin wax and inorganic scale by at least 40%, preferably at least50%, as compared to the interior surface of said oil pipe without saidlining being present. These reductions are also made in comparison topipe lined with only an epoxy resin on the interior surface of the pipe.

In fact, reductions of at least 60%, 70%, 80% and even at least 90% havebeen realized. Preferably these reductions apply to at least two of thedeposition materials, and more preferably, to all three of them. Thus,in accordance with the present invention, there is also provided amethod for reducing the deposition in a rigid oil well pipe of at leastone of asphaltenes, paraffin wax, and inorganic scale by at least 40% ascompared to the interior surface of said oil pipe without the linerbeing present. In addition, the preformed liner provides corrosionprotection to the interior surface of the pipe.

In use, the pipes are assembled together, end to end, by conventionaltechniques dependent on the utility. The type of lining that is used ineach pipe or section of pipe is tailored according to the demands of thesystem in accordance with the present invention. In oil wells pipes willtypically have screw sections at each end so that length after length ofcoated pipe can be screwed together to reach the depth of the oil well.The lining will be applied to abutting ends of the screw threads so thatwhen screwed together, the succession of pipes present a continuousnon-stick surface to the oil. For oil pipelines, the pipes may haveflanges for bolting together to form the continuous succession of pipesrequired. In that case, the coating of the interior surface of the pipeis extended to the surface of the flange so that the butting together ofthe flanges adds to the continuity of the coating on the interiorsurface of the pipes.

Test Methods

Paraffin Deposition Test

A cold finger apparatus, available at Westport Technology CenterInternational (Houston, Tex.) is used to test the baked coatings asprepared in the Examples for the degree of release (non-stick) theyexhibit. The apparatus includes a circulating beaker (double-walled)filled with mineral oil and connected to a first temperature bath whichis placed on a magnetic mixing plate. A stainless steel cup with amagnetic stirring bar is submerged in the mineral oil and thetemperature set to 140° F. (60° C.). A cold finger (tubular projection)is connected to a second water circulating temperature bath, and thetemperature set to 60° F.

Stainless steel sleeves (6″ long, 0.5″ inside ID, 0.625″ OD) closed flatat the bottom which are coated as described in the Examples are washedwith solvent (toluene, then methanol) and placed in a hot oven to ensurea clean surface for wax to deposit on. The sleeve is then weighed,secured over the finger with a set screw at the top to create a tightfit, and allowed to cool for thirty minutes. After thirty minutes, thesleeve is attached over the cold finger in a tight fit and submerged inthe crude oil for twenty-four hours.

Crude oil known to have a large wax content with a wax appearancetemperature of approximately 105° F. is used for this test. The crude isinitially heated to 150° F. (66° C.) and centrifuged twice to remove anywater and sediments. The source sample of crude was maintained at 150°F. (66° C.) during the duration of the testing to ensure the waxremained in solution.

At the completion of the twenty-four hour test time, the sleeve isremoved from the crude and allowed to sit for one hour at 60° F. (16°C.) in a nitrogen environment. A final weight is measured. Weight datacollected before and after submersion are used to calculate the waxdeposition on the sleeve. From the material balance a mass per unit areawas calculated for comparison purposes. The baseline for comparison isthe paraffin adhesion test performed on commercially availableepoxy-resin coated oil pipe, wherein the deposition of paraffin on theepoxy resin coating amounted to 0.0652 g/cm².

Adhesion Tests

Test panels of cold rolled steel 4.0″×12.0″ (10.1 cm×30.5 cm) panels arecleaned with an acetone rinse. The panel has a grit blast surface. Thepanels are coated according to the description in each of the examples.The panels are subjected to the following two adhesion tests.

(1) Post Boiling Water Fingernail Adhesion (PWA)

Coated test panels are submerged in boiling water for 20 minutes. Thewater is allowed to come to a full boil after inserting the coatedpanel, before timing is begun. After the boiling water treatment, thepanel is cooled to room temperature and dried thoroughly. The fingernailscratch test involves the use of the fingernail, to chip or peel awaythe coating from the edge of a deliberate knife scratch in the film, totest the degree of adhesion of the film. If the coating can be pulledaway from the substrate for 1 cm or more, the coating is considered tofail the PWA test. If the coating cannot be pulled loose for a distanceof 1 cm, the coating is considered to pass the PWA test.

(2) Cross-Hatch Adhesion

Coated substrates are subjected to a cross-hatch (x-hatch) test foradhesion. The coated sample is scribed with a razor blade, aided by astainless steel template, to make 11 parallel cuts about 3/32 inch (2.4mm) apart through the film to the metal surface. This procedure isrepeated at right angles to the first cuts to produce a grid of 100squares. The coated and scribed sample is immersed in boiling water for20 minutes, and then is removed from the water and cooled to roomtemperature without quenching the sample. Then a strip of transparenttape (3M Brand No. 898), 0.75 by 2.16 inch (1.9 by 5.5 cm), is pressedfirmly over the scribed area with the tape oriented in a paralleldirection to the scribed lines. The tape is then pulled off at a 90°angle rapidly but without jerking. This step is repeated at a 90° angleto the first step with a fresh piece of tape, and then repeated twotimes more again at 90° angles to the previous step, each time with afresh piece of tape. Passing the test requires that no squares beremoved from the 100-square grid.

EXAMPLES

The following Examples illustrate the effects of the present inventionon coupons which are coated with interior coatings according to thepresent invention.

In the following Examples, substrates for coating are cleaned by baking30 min @ 800° F. (427° C.) and grit blasted with 40 grit aluminum oxide)to a roughness of approximately 70-125 microinches Ra. Liquid coatingsare applied by using a spray gun, Model Number MSA-510 available fromDeVilbiss located in Glendale Heights, Ill. Powder coatings are appliedby using Nordson manual electrostatic powder spray guns, ModelVersa-Spray I located in Amhearst, Ohio.

For determining the degree of release of the coatings, the substratebeing coated is a stainless steel sleeve suitable for use in theapparatus described above in the Paraffin Deposition Test. Fordetermining the adhesion quality, the substrate being coated is a carbonsteel panel suitable for use in the PWA Test and the Cross-HatchAdhesion Test described above.

The primer layers formed in the Examples have the following pre-bakecompositions: TABLE 1 Liquid Primers Primer 1 2 3 Ingredient Wt % wt %wt % Fluoropolymer FEP 12.5 10.9 ETFE 20.7 Polymer binder Polyamideimide1.1 3.7 11.9 Polyethersulfone 7.6 Polyphenylene Sulfide 3.4 SolventsNMP* 47.8 1.9 40.7 Other Organics** 20.1 4.7 32.0 Water 60.2 Pigments9.9 4.2 1.7 Dispersing Agent 1.0 1.2 2.8 Total 100 100 100*NMP is N-methyl-2-pyrrolidone**Other organics may include solvents such as MIBK (methyl isobutylketone), hydrocarbons such as heavy naphtha, xylene etc., furfurylalcohol, triethanol amine or mixtures thereof.FEP: TFE/HFP fluoropolymer containing 11-12.5 wt % HFP, an averageparticle size of 8 micrometers and a melt flow rate of 6.8-7.8 g/10 minmeasured at 372° C. by the method of ASTM D-1238.ETFE: E/TFE/PFBE fluoropolymer containing 19-21 wt % ethylene and 3-4.5wt % PFBE having average particle size of 8 micrometers and a melt flowrate of 6-8 g/10 min measured at 298° C. by the method of ASTM D-1238.

The overcoat layers formed in the Examples have the following pre-bakecompositions: TABLE 2 Powder Overcoats Overcoat A B 1 2 Ingredient wt %wt % wt % wt % Epoxy 100 ETFE 100 Perfluoropolymers PFA FEP PFAFluorinated 100 PFA Modified PEVE 100 Stabilizer (Zn) Total 100 100 100100 Overcoat 4 5 6 Ingredient wt % wt % wt % Epoxy ETFEPerfluoropolymers PFA 99.2 100 FEP 100 PFA Fluorinated PFA Modified PEVEStabilizer (Zn) 0.8 Total 100 100 100FEP: TFE/HFP fluoropolymer resin containing 11-12.5 wt % HFP having amelt flow rate of 6.8-7.8 g/10 min and an average particle size of 35micrometers.PFA: TFE/PPVE fluoropolymer resin containing 3.8-4.8 wt % PPVE having amelt flow rate of 10-17 g/10 min and an average particle size of 35micrometers.PFA modified with PEVE: TFE/PPVE/PEVE fluoropolymer resin containing6.8-7.8 wt % PEVE prepared according to the teachings of U.S. Pat. No.5,932,673 (Aten et al./DuPont) having a melt flow rate of 13-18 g/10 minand an average particle size of 8 micrometers.PFA Fluorinated: TFE/PPVE fluoropolymer resin containing 3.8-4.8 wt %PPVE prepared according to the teachings of US patent 4,743,658(Imbalzano et al./DuPont) having a melt flow rate of 12-20 g/10 min andan average particle size range of 25 micrometers.PFA: TFE/PPVE fluoropolymer resin containing 3.8-4.8 wt % PPVE having amelt flow rate of 10-17 g/10 min and an average particle size of 35micrometers.

TABLE 3 Liquid Overcoat Overcoat 3 Ingredient wt % Perfluoropolymer PFA45.0 Other Organics 0.6 Water 43.8 Thickener 10.1 Dispersing Agents 0.5Total 100

TABLE 4 Liquid Midcoat Midcoat 1 Ingredient wt % Perfluoropolymer PFA41.2 Glycerine 8.3 Water 42.8 Red Mica 3.9 Thickener 1.1 DispersingAgents 0.4 Other Organics 1.1 Tin Metal 1.2 Total 100.0

The baking conditions are set forth in the Examples. Good adhesion ofthe primer layer to the substrate and of the primer layer to theovercoat layer is indicated by their performance in the PWA Test and theCross-Hatch Adhesion Test.

The non-stick characteristic of the baked coatings in the Examples areconfirmed by subjecting the coatings to the paraffin deposition test asdescribed above. The baseline for comparison is the paraffin depositiontest performed on commercially available epoxy-resin coated oil pipe,wherein the deposition of paraffin on the epoxy resin coating amountedto 0.0652 g/cm². The examples of this invention all have coatings with awax deposition below that of standard epoxy resin coating.

Comparative Example A

Epoxy Standard

A layer of coating A (epoxy powder) is applied to a prepared stainlesssteel sleeve, followed by baking at 316° C. for 20 minutes. The dry filmthickness (DFT) of the paint layer is 100-125 micrometers. When thecoated sleeve is subjected to the Paraffin Deposition Test, a depositionof 0.0652 g/cm² is obtained.

Comparative Example B ETFE Primer/ETFE Overcoat

A layer of primer 2 (aqueous ETFE) is applied to a prepared stainlesssteel sleeve and a prepared carbon steel panel, followed by baking at150° C. for 10 minutes. The dry film thickness (DFT) of the primer layeris 12-19 micrometers (p). A layer of overcoat B (powder ETFE) is appliedover the dried primer layer. It is baked at 316° C. for 20 minutes. Thetotal DFT is 100-125 micrometers and the total thickness of the overcoatis 81-113 micrometers. When the coated sleeve is subjected to theParaffin Deposition Test, a deposition of 0.0327 g/cm² is obtained. Whenthe coated carbon steel panel is subjected to the PWA test andCross-Hatch Adhesion Test, the panel passes both tests.

Aqueous primers are not preferred for use in this invention because ofthe potential for reduced corrosion resistance over a prolonged periodof time. ETFE overcoats are inferior to the perfluoropolymer overcoatsof this invention.

Comparative Example C Uncoated Substrate

An uncoated prepared stainless steel sleeve is subjected to the ParaffinDeposition Test, a deposition of 0.0296 g/cm² is obtained.

Example 1 FEP Primer/Modified PFA Overcoat

A layer of primer 1 (liquid FEP) is applied to a prepared stainlesssteel sleeve and a prepared carbon steel panel, followed by baking at150° C. for 10 minutes. The dry film thickness (DFT) of the primer layeris 12-19 micrometers. A layer of overcoat 1 (PFA modified with PEVEpowder) is applied over the dried primer layer. It is baked at 399° C.for 20 minutes. The total DFT is 60-75 micrometers. A second layer ofovercoat is applied. It is baked at 371° C. for 20 minutes. The totalDFT is 100-125 micrometers and the total thickness of the overcoat is81-113 micrometers. An insulating layer is applied to the exterior ofthe sleeve.

When the coated sleeve is subjected to the Paraffin Deposition Test, adeposition of only 0.0168 g/cm² is obtained. When the coated carbonsteel panel is subjected to the PWA test and Cross-Hatch Adhesion Test,the panel passes both tests.

Example 2 FEP Primer/Fluorinated PFA Overcoat

A layer of primer 1 (liquid FEP) is applied to a prepared stainlesssteel sleeve and a prepared carbon steel panel, followed by baking at150° C. for 10 minutes. The dry film thickness (DFT) of the primer layeris 12-19 micrometers. A layer of overcoat 2 (fluorinated PFA powder) isapplied over the dried primer layer. It is baked at 399° C. for 20minutes. The total DFT is 60-75 micrometers. A second layer of overcoat2 is applied. It is baked at 371° C. for 20 minutes. The total DFT is100-125 micrometers and the total thickness of the overcoat is 81-113micrometers.

When the coated sleeve is subjected to the Paraffin Deposition Test, adeposition of only 0.0145 g/cm² is obtained. When the coated carbonsteel panel is subjected to the PWA test and Cross-Hatch Adhesion Test,the panel passes both tests.

Example 3 FEP Primer/PFA Overcoat

A layer of primer 1 (liquid FEP) is applied to a prepared stainlesssteel sleeve and a prepared carbon steel panel, followed by baking at150° C. for 10 minutes. The dry film thickness (DFT) of the primer layeris 12-19 micrometers. A layer of overcoat 3 (PFA liquid) is applied overthe dried primer layer. It is baked at 399° C. for 20 minutes. The totalDFT is 60-75 micrometers. A second layer of overcoat 3 is applied. It isbaked at 371° C. for 20 minutes. The total DFT is 100-125 micrometersand the total thickness of the overcoat is 81-113 micrometers. When thecoated sleeve is subjected to the Paraffin Deposition Test, a depositionof only 0.0124 g/cm² is obtained. When the coated carbon steel panel issubjected to the PWA test and Cross-Hatch Adhesion Test, the panelpasses both tests.

Example 4 FEP Primer/PFA Overcoat

A layer of primer 1 (liquid FEP) is applied to a prepared stainlesssteel sleeve and a prepared carbon steel panel, followed by baking at150° C. for 10 minutes. The dry film thickness (DFT) of the primer layeris 12-19 micrometers. A layer of overcoat 4 (PFA powder) is applied overthe dried primer layer. It is baked at 399° C. for 20 minutes. The totalDFT is 60-75 micrometers. A second layer of overcoat 4 is applied. It isbaked at 371° C. for 20 minutes. The total DFT is 100-125 micrometersand the total thickness of the overcoat is 81-113 micrometers.

When the coated sleeve is subjected to the Paraffin Deposition Test, adeposition of only 0.0124 g/cm² is obtained. When the coated carbonsteel panel is subjected to the PWA test and Cross-Hatch Adhesion Test,the panel passes both tests.

Example 5 FEP Primer/PFA Overcoat

A layer of primer 1 (liquid FEP) is applied to a prepared stainlesssteel sleeve and a prepared carbon steel panel, followed by baking at150° C. for 10 minutes. The dry film thickness (DFT) of the primer layeris 12-19 micrometers. A layer of overcoat 5 (PFA powder) is applied overthe dried primer layer. It is baked at 399° C. for 20 minutes. The totalDFT is 60-75 micrometers. A second layer of overcoat 5 is applied. It isbaked at 371° C. for 20 minutes. The total DFT is 100-125 micrometersand the total thickness of the overcoat is 81-113 micrometers.

When the coated sleeve is subjected to the Paraffin Deposition Test, adeposition of only 0.0116 g/cm² is obtained. When the coated carbonsteel panel is subjected to the PWA test and Cross-Hatch Adhesion Test,the panel passes both tests.

Example 6 FEP Primer/FEP Overcoat

A layer of primer 1 (liquid FEP) is applied to a prepared stainlesssteel sleeve and a prepared carbon steel panel, followed by baking at150° C. for 10 minutes. The dry film thickness (DFT) of the primer layeris 12-19 micrometers. A layer of overcoat 6 (FEP powder) is applied overthe dried primer layer. It is baked at 399° C. for 20 minutes. The totalDFT is 60-75 micrometers. A second layer of overcoat 6 is applied. It isbaked at 371° C. for 20 minutes. The total DFT is 100-125 micrometersand the total thickness of the overcoat is 81-113 micrometers.

When the coated sleeve is subjected to the Paraffin Deposition Test, adeposition of only 0.0110 g/cm² is obtained. When the coated carbonsteel panel is subjected to the PWA test and Cross-Hatch Adhesion Test,the panel passes both tests.

Example 7 FEP Primer/PFA Overcoat

A layer of primer 1 (liquid FEP) is applied to a prepared stainlesssteel sleeve and a prepared carbon steel panel, followed by baking at150° C. for 10 minutes. The dry film thickness (DFT) of the primer layeris 12-19 micrometers. A layer of overcoat 5 (PFA powder) is applied overthe dried primer layer. It is baked at 399° C. for 20 minutes. The totalDFT is 60-75 micrometers. A second layer of overcoat 5 is applied. It isbaked at 371° C. for 20 minutes. Additional layers of overcoat 1 areapplied and baked at 343° C. for 20 minutes until the total DFT is950-1050 micrometers and the total thickness of the overcoat is 931-1038micrometers.

When the coated sleeve is subjected to the Paraffin Deposition Test, adeposition of only 0.0098 g/cm² is obtained. When the coated carbonsteel panel is subjected to the PWA test and Cross-Hatch Adhesion Test,the panel passes both tests.

Example 8 FEP/PFA Overcoat

A layer of primer 1 (liquid FEP) is applied to a prepared stainlesssteel sleeve and a prepared carbon steel panel, followed by baking at150° C. for 10 minutes. The dry film thickness (DFT) of the primer layeris 12-19 micrometers. A layer of overcoat 2 is applied over the driedprimer layer. It is baked at 399° C. for 20 minutes. The total DFT is60-75 micrometers. A second layer of overcoat 2 (fluorinated PFA) isapplied. It is baked at 371° C. for 20 minutes. Additional layers ofovercoat 4 are applied and baked at 343° C. for 20 minutes until thetotal DFT is 950-1050 micrometers and the total thickness of theovercoat is 931-1038 micrometers.

When the coated sleeve is subjected to the Paraffin Deposition Test, adeposition of only 0.0042 g/cm² is obtained. When the coated carbonsteel panel is subjected to the PWA test and Cross-Hatch Adhesion Test,the panel passes both tests.

Example 9 FEP Primer/PFA Overcoat

A layer of primer 3 (liquid FEP) is applied to a prepared stainlesssteel sleeve and a prepared carbon steel panel, followed by baking at150° C. for 10 minutes. The dry film thickness (DFT) of the primer layeris 8-12 micrometers. A layer of overcoat 2 (fluorinated PFA) is appliedover the dried primer layer. It is baked at 399° C. for 20 minutes. Thetotal DFT is 60-70 micrometers. A second layer of overcoat 2(fluorinated PFA) is applied. The total DFT is 80-110 micrometers andthe total thickness of the overcoat is 68-102 micrometers. It is bakedat 371° C. for 20 minutes.

When the coated sleeve is subjected to the Paraffin Deposition Test, adeposition of only 0.0042 g/cm² is obtained. When the coated carbonsteel panel is subjected to the PWA test and Cross-Hatch Adhesion Test,the panel passes both tests.

Example 10 FEP Primer/PFA Rotolined Overcoat

A carbon steel pipe suitable for conveying oil having a diameter of 3inches (7.6 micrometers) and a length of 30 feet (9 m) is cleaned bybaking 30 min @ 800° F. (427° C.) and grit blasted with 40 grit aluminumoxide to a roughness of approximately 70-125 microinches Ra. A layer ofprimer 1 is applied to the interior of the pipe, followed by baking at atemperature of 750° F. (399° C.) for five minutes to dry and fully bake(cure) the primer. The dry film thickness (DFT) of the primer layer is8-12 micrometers. The primed pipe is rotolined with a compositioncontaining a commercially available copolymer of TFE/PPVE powder havingan MFR of 6 g/10 min and an average particle size of 475 μm that hasbeen stabilized (fluorinated according to the teachings of U.S. Pat. No.4,743,658 Imbalzano et al./DuPont). The powder composition is introducedto the interior of the pipe to be rotolined in the amount sufficient toobtain an overcoat lining thickness of 30 mils (762 micrometers). Thepipe is temporarily closed at both ends and mounted on a mechanism thatboth rocks and rotates the pipe within in an air oven. The mechanism iscommercially available as a Rock and Roll machine. The pipe is heatedabove the melting point of the copolymer particles of the overcoat andis rotated around its longitudinal axis during the heating while beingrocked from end to end during the rotation at a temperature 740° F.(380° C.) for 120 min of pipe rotation. Despite, the long exposure tohigh temperature, the primer is surprisingly not degraded and stillfunctions to adhere the coating to the pipe's interior. The pipe isrotated in an air oven resulting in lining the interior surface of thepipe with a coating of uniform distribution. Upon completion of therotolining process, the oven is cooled and the rotolined pipe isexamined for the quality of the rotolining. The temporary ends areremoved from the pipe and the bubble-free quality of the lining isdetermined by observation of the lining with the naked eye. The liningis considered bubble free when no bubbles are visible within the liningthickness and the surface of the lining is smooth, i.e. free of voids,lumps, and craters.

For determining the adhesion quality, the coated pipe is sectioned andsubjected to the PWA Test and the Cross-Hatch Adhesion Test as describedabove, except only an “X” is scribed in the Cross Hatch Test instead ofa grid. The pipe sections tested herein pass the PWA test and no liningis removed with the Cross Hatch Test.

Example 11 Inorganic Scale Deposition Test

A number of the overcoats (FEP and PFA) from the foregoing Examples weresubjected to coupon immersion testing in brine solutions in order todetermine the reduction in inorganic scale deposition of the coatedcoupon, with the result being that scale deposition was reduced by morethan 50 wt % as compared to the uncoated coupons. These tests were doneby soaking coated and uncoated steel coupons in calcite and barite brinesolutions having the following compositions: Brine A g/kg water Brine Bg/kg CaCl₂.2H₂O 36.87 same 8.6 KCl 11.43 same 4.38 MgCl₂.6H₂O 1.8 same0.41 NaCl 138.9 same 89.09 Na₂SO₄ 0.32 — — BaCl₂ 3.08The coupons were suspended for two days under 100 psi (6.9 MPa) pressurein either in Brine A heated at 140 F (60° C.) or in Brine B heated at90° F. (32° C.) and the weight pickups (scale deposition) for the coatedcoupons were compared to that for the uncoated steel coupons to revealthe reduction in scale deposition for the coupons coated with linings ofthe present invention.

Example 12 Asphaltene Deposition Test

Asphaltene is a mixture of amorphous high molecular weight, polynucleararomatic compounds, containing C, H, O, N, and S, and often metals suchas V or Ni. Asphaltene is soluble in oil, but becomes insoluble withdrop in pressure, change in pH, or solvency change such as occurs in oilpipe utility. Asphaltene deposition can be measured by the flow loopmethod as practiced by the Petroleum Research Center located at the NewMexico Institute of Mining and technology in Socorro, N. Mex. Briefly,the material to be tested is formed into a loop and oil is flowedthrough the loop under conditions to cause the asphaltene in the oil tobecome insoluble, so that it has a chance to deposit on the interiorsurface of the loop. The deposition of asphaltene is determined byweighing the loop after the flow experiment is completed, comparing suchweight with the weight of the loop before the flow test. In greaterdetail, the loop being tested is a tube that 100 ft (30.5 m) long andhas an interior diameter of 0.03 in (0.75 mm) and is made of either oneof the overcoat perfluoropolymers disclosed in the foregoing Examples orof steel. The tube is formed into a coil (loop), like a spring, so thatit will fit into a water bath maintained at 60° C. A 50/50 vol % mixtureof asphaltene-containing oil and n-pentadecane solvent is meteredthrough the loop at a rate of 0.24 ml/hr for 24 hrs. The oil tested hadthe following characteristics: API gravity of 28.80, viscosity of 30 cPat 20°, and was composed of 51.1% saturates, 28.3% aromatics, 14.5%resins, 6.1% asphaltenes and contained 19 ppm Ni and 187 ppm V. For theuncoated steel loop, the weight gain from deposited asphaltene is 0.51g, while for FEP and the fluorinated PFA of Example 8, there is noweight gain, indicating the effectiveness of the perfluoropolymer toreduce asphaltene deposition.

Example 13 Salt Water Permeation Test

This test is conducted to determine the salt water permeability ofperfluoropolymers as compared to epoxy resin by exposing 5 mil (127micrometers) thick coatings of these materials on steel coupons to saltwater under severe conditions and subjecting the so-exposed coupons tothe well-known Log Z-Electrical Impedance Spectroscopy. Impedance of thecoating before and after the exposure is compared. A reduction inimpedance indicates the permeability of the coating. In greater detail,the coated coupons are suspended in an autoclave having: 1) an aqueousphase with a 5 wt % aqueous solution of NaCl, 2) an organic phase with50 volume % kerosene and 50 volume % toluene, and 3) a gas phase with 5volume % hydrogen sulfide (H₂S), 5 volume % carbon dioxide (CO₂) and 90volume % methane (CH₄), which is maintained at approximately 251° F.(122° C.) therein in contact with a portion of the coating. Theautoclave is maintained at 251° F. (122° C.) and 1026 psi (70.8 MPa) for29 days. The impedance of the coating is measured (before and after saltwater exposure) using an electrochemical cell consisting of the coatedcoupon, a reference electrode, and an inert counter electrode. Theelectronic measuring equipment consists of a potentiostat, a frequencyresponse analyzer and a computer with electrical impedance spectroscopysoftware. Impedance of the coating is measured as a function of thefrequency of the applied AC voltage. The frequency ranges from 0.001 to100 kHz. The resulting data is presented in the form of a Bode plot,consisting of Log Z plotted versus Log f, where Z is the impedance inohms cm and f is frequency in Hertz. The comparison in impedance resultsis taken a 0.1 of the Bode plot, as follows: Log Z impedance CoatingBefore Exposure After Exposure PFA 11.0 10.9 FEP 11.0 11.0 Epoxy 10.87.1Tests of a one-coat system of FEP/PES which could only be applied to athickness of 2 mils, are subjected to the same Autoclave conditions, andresult in a Log Z impedance before exposure of 9.4, and after exposure,of 5.8.

The 34% decrease in impedance for the epoxy resin coating represents asubstantial permeability of this coating to the salt water, and indeedthe coating had blistered in places from the underlying steel coupon. Incontrast, the impedance of perfluoropolymer coatings with no binder issubstantially unchanged and there is no separation (no blistering) ofthe coating from the steel coupon, indicating substantial impermeabilityof these coatings to the salt water. This substantial impermeability cantherefore be characterized by the absence of coating separation of thecoating from the steel coupon or quantitatively by the reduction in LogZ impedance of less than 10%, preferably less than 5%. When the coatedcoupons are subjected to H₂S gas and methane/toluene liquid mixture inthe same autoclave under the same conditions as the salt water testing,no change in the coatings is noticed, indicating the greater severity ofthe salt water exposure.

Example 14 Single Layer Coating

Primer 1 is used a single layer coating on the coupon and tested as setforth in Example 11. Despite the presence of non-fluorine containingpolymer binder (polyamideimide and polyether sulfone) in the primercomposition, the deposition of inorganic scale on the coating is muchless than for the bare steel coupon and about the same as for the FEPovercoat.

1. A system of pipes for conveying flowable media comprising a firstpipe and a second pipe having a lining adhered to the interior surfaceof the pipe, and the lining of the second pipe comprises a primer layeradhered to the interior surface of the pipe and an overcoat or apreformed film comprising a fluoropolymer adhered to the primer layer.2. A system of pipes for conveying flowable media comprising a firstpipe and a second pipe having a lining adhered to the interior surfaceof the pipe, and the lining of the second pipe consists essentially of aperfluoropolymer.
 3. A system of pipes for conveying flowable mediacomprising a first pipe and a second pipe having a lining adhered to theinterior surface of the pipe, and the lining of the second pipecomprises a barrier layer including a plurality of particles which forma mechanical barrier against permeation of water, gas and solvents tothe pipe.
 4. The system of claims 1, 2 or 3, wherein the first pipe isunlined.
 5. The system of claims 1, 2 or 3, wherein the first pipe islined with a different material than the second pipe.
 6. The system ofclaim 3, wherein the different material of the first pipe comprisesfluorinated ethylene propylene.
 7. The system of claim 3, wherein thedifferent material of the first pipe comprises epoxy.
 8. The system ofclaim 2, wherein the primer layer comprises a perfluoropolymer.
 9. Thesystem of claim 8, wherein the overcoat also comprise aperfluoropolymer.
 10. The system of claims 1, 2 or 3, wherein thethickness of the lining in the section of the pipe at a depth of 1500feet or greater below the surface is 5 mil.
 11. The system of claims 1,2 or 3, wherein the thickness of the lining in the section of the pipeat a depth of 1500 feet or less is 40-50 mils.